fix(streamable-http): close SSE responses on errors #2156

Job	Run time
checks / pre-commit	32s
checks / readme-snippets	11s
checks / test (3.11, lowest-direct, ubuntu-latest)	54s
checks / test (3.11, lowest-direct, windows-latest)	3m 8s
checks / test (3.11, locked, windows-latest)	2m 11s
checks / test (3.14, locked, windows-latest)	3m 10s
checks / test (3.13, locked, ubuntu-latest)	48s
checks / test (3.14, locked, ubuntu-latest)	2m 28s
checks / test (3.13, lowest-direct, windows-latest)	2m 33s
checks / test (3.12, locked, windows-latest)	3m 23s
checks / test (3.12, lowest-direct, windows-latest)	3m 37s
checks / test (3.11, locked, ubuntu-latest)	49s
checks / test (3.10, lowest-direct, ubuntu-latest)	54s
checks / test (3.10, locked, windows-latest)	2m 33s
checks / test (3.14, lowest-direct, windows-latest)	2m 20s
checks / test (3.10, lowest-direct, windows-latest)	2m 28s
checks / test (3.10, locked, ubuntu-latest)	52s
checks / test (3.13, locked, windows-latest)	2m 34s
checks / test (3.13, lowest-direct, ubuntu-latest)	55s
checks / test (3.12, lowest-direct, ubuntu-latest)	58s
checks / test (3.12, locked, ubuntu-latest)	56s
checks / test (3.14, lowest-direct, ubuntu-latest)	1m 21s
all-green	3s
	39m 38s

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